See explanation.

The converse of the Isosceles Triangle Theorem states that if two angles ##hat A## and ##hat B## of a triangle ##ABC## are congruent then the two sides ##BC## and ##AC## opposite to these angles are congruent.

The proof is very quick: if we trace the bisector of ##hat C## that meets the opposite side ##AB## in a point ##P## we get that the angles ##hat(ACP)## and ##hat(BCP)## are congruent.

We can prove that the triangles ##ACP## and ##BCP## are congruent. In fact the hypotheses of the AAS criterion are satisfied:

Since the triangles ##ACP## and ##BCP## are congruent we conclude that ##BC cong AC##.